Pros or cons ?
At the US price, there are no cons.
It will do what it says. You've gotta have a plastic that's friendly to this sort of thing, and the strength/durability/appearance of the repair will vary greatly from one plastic to another. Just like it says, you heat that wire and melt it into the plastic a little ways. You'll want some GOOD flush cutting side cutters, as the ones pictured are gonna leave "stumps". You want as little sticking up as possible. Try taking the end of a brad nail and sanding it flat. Then do it without scratching the surface it's flush to..... It's an adventure to figure some of that stuff out. Then, all the holes you've melted the staples into, those have to be "smoothed" with the flat gadget. Picture smoothing out scratched plastic with a butter knife that you've heated with a propane torch...
It's kind of an art form, and it WILL produce acceptable results in a TON of applications. It will not produce new plastic, and it's a challenge to make broken plastic look new. This is not a fault of the tool, it's a characteristic of the plastic.
Now that I've made it sound like something that should be passed up.... No, that's not my intention. These do what they say. Get one if you think you might have a use. It's just not the fast, easy, and faultless as they are in the idealized advertisements. But they're a good thing to have. Mine (another brand, same crap) has brought both joy and tears. 99 percent of the tears though were from finding out "sooner than I would have liked to" that the plastic in question was meltable but not really repairable, and from the lack of knowledge of the art form of smoothing and forming plastic to look "passable" after repair. Seriously, broken plastic equals nothing to loose by trying. You'll get some big saves, to cover the tool, and you'll get some big disappointments. The successes are great, and the failures were already "dead", you just didn't know it yet.
FWIW, the stainless "staples" are manditory, even if you do a DIY route with a soldering gun. (I have no idea if that even works...) Paperclips rot out no many how many layers of paint go on it, they shatter at the mention of vibration, and are generally ill suited. Although they WILL melt right in. Not that I've checked.